1. Field of the Invention
The present invention relates to an optical actuator, and, more particularly, to an optical actuator for controlling the position of a miniature optical pickup modularized so that an objective lens and an optical system are moved together.
2. Description of the Related Art
An optical pickup used for typical optical disk drives, such as CD players or DVD players, includes a fixed unit having optical elements such as a laser diode emitting light toward a recording medium, or a photodiode receiving the light reflected by the recording medium, a mobile unit having an objective lens focusing light emitted from the laser diode on the recording medium, and an actuator performing an accurate positional control of the light, that is, the focus and tracking control of the light through the objective lens, by adjusting the position of the mobile unit.
A smaller structure of the optical disk drive is needed for portable apparatuses such as notebook computers or PDAs. Accordingly, a miniature optical pickup is adopted in which the fixed unit and the mobile unit of the optical pickup are integrally formed as a module so that the whole unit is controlled in a focus direction and a tracking direction.
FIG. 1 shows the structure of a conventional actuator for the focus and tracking control of the miniature optical pickup.
Referring to the drawing, a swing arm 11 is provided that is capable of rotating in a direction T around a rotation shaft 10a provided on a base 10. A voice coil motor 12 is installed to rotate the swing arm 11 by an electromagnetic force. The voice coil motor 12 includes a coil 12c installed at one side of the swing arm 11, and a magnet 12a and a yoke 12b disposed under the coil 12c. This swing mechanism has the same structure as that of a hard disk drive for transferring a magnetic head, and is used for movement of the optical pickup 13 between tracks and a fine tracking control.
A pivot arm 16 having a miniature optical pickup 13 mounted thereon is coupled to the other side of the swing arm 11. That is, the swing arm 11 and the pivot arm 16 are coupled as both ends of a leaf spring 14 are inserted in one end portion of each of the swing arm 11 and the pivot arm 16, respectively. Accordingly, the pivot arm 16, which is supported by the swing arm 11, can pivot in a direction F. A focus coil 15a, generating an electromagnetic force for the pivot movement in an interaction with the magnet 15b installed on the base 10, is installed on a lower surface of the pivot arm 16.
Thus, for the movement of the optical pickup 13 between tracks and the tracking control, the voice coil motor 12 is operated to rotate the swing arm 11 in the direction T. For the focus control, the pivot arm 16 is rotated in the direction F by applying current to the focus coil 15a so as to move the optical pickup 13. A structure similar to that of a conventional optical pickup actuator is disclosed in PCT Publication No. WO 02/29792 A2.
However, in the above structure, the driving body moving to perform the focus control and the tracking control is too large. That is, the pivot arm 16, supported by the swing arm 11, moves up and down for the focus control, and the swing arm 11 rotates to the left and right, together with the pivot arm 16, for the tracking control. Since the weight of the driving body is heavy in both cases, the sensitivity of control is deteriorated. In particular, since the entire portion of the swing arm 11 must be rotated for the tracking control, a fine control is very difficult.
Therefore, an optical pickup actuator having an improved structure overcoming the above problems is required.